Conversion of mineral oil stocks



Dec. 2, 1941. D. e. BRANDT I CONVERSION OF MINERAL OIL STOCKS Filed Nov. 30, 1938 GASOLINE INVENTOR DAV/0 G. BRANDT ATTORNEY HTHA FUEL on.

III

REACTION CHAMBER Patented Dec. 2, 1941 CONVERSION OF MKNERAL OIL STOCKS David G. Brandt, Westfield, N. J., assignor to Cities Service Oil Company, New York, N. Y., a corporation of Pennsylvania Application November 30, 1938, Serial No. 243,056

6 Claims.

This invention relates to a process for converting petroleum oils of varying boiling ranges into gasoline suitable for use in internal combustion engines having high compression ratios.

This application is a continuation-in-part of application Serial No. 720,539, filed April 14, 1934, and application Serial No. 158,900, filed August 13, 1937, for a Process for conversion of hydrocarbon. In accordance with the disclosure of the latter pending application, the process described and claimed therein includes the simultaneous heating of a distillate such as butane and a heavy distillate such as gas oil in separate heating zones in which the butane is heated to a higher temperature than that to which the gas oil is heated. In these two heating zones the distillates are preferably subjected to suflicient cracking temperature and pressure to produce a maximum of unsaturated olefin type hydrocarbons without causing substantial polymerization. The products from these zones are mixed and then subjected to further heating and conversion conditio-ns to cause interpolymerization of the constituents of the mixture. This operation is carried out While the mixture passes through a heating coil after which the mixture is passed into an enlarged reaction chamber. After the mixture has been subjected to the desired conversion, the products are quicldy cooled to a temperature adapted to prevent coke formation and condense any residual oil constituents which may be present.

In accordance with the further disclosure of application Serial No. 158,900, the vapors remaining uncondensed after the quick cooling operation, are conducted to a fractionating tower from which the gasoline constituents are taken overhead, condensed, separated from uncondensed gases at relatively high pressure, and stabilized in a fractionating tower. In the stabilizing operation a portion of the C4 hydrocarbons and all lower boiling hydrocarbons are removed overhead from the stabilizer and subjected to condensing conditions to form a condensate. This condensate is conducted to the butane conversion zone, and reflux distillate from the first fractionating tower is sent to the heavier oil conversion zone.

Application Serial No. 720,539 discloses a cracking operation in which high temperature conversion products are introduced into the upper portion of an enlarged vertical reaction chamber and passed downwardly therethrough to the bottom of the chamber from which they are discharged through a funnel-like structure. As the high temperature products enter the funnel, they are suddenly chilled to a temperature below that at which coke formation takes place by spraying a relatively heavy oil directly into the vapors, so that there is no substantial formation of coke. The products discharged through the funnel pass into a separating chamber from which vapors are separated from liquid, the liquid being withdrawn into a low pressure concentrator for the production of fuel oil and a concentrator distillate. The vapors from the concentrator are condensed as a single distillate and used as the cooling medium sprayed into the funnel structure. Any excess of this concentrator distillate is brought in contact with the vapors separated out in the separating chamber below the funnel, after which the vapors are passed into the lower portion of a iractionating column where they pass in indirect heat exchange with crude oil charging stock. 7

The process disclosed in application Serial No. 720,539 also includes the passage of reflux condensate from the fractionating column and crude oil bottoms through a heating coil in which the mixture is heated to a temperature sufiicient to vaporize a substantial portion thereof. The resulting heated products are conducted into an enlarged separating chamber in which the residue is separated from the resulting vapors. This residue is conducted to the concentrator along with the unvaporized oil constituents produced in the sudden chilling operation. The vapors separated out in the enlarged separating chamber are then passed through cracking coils and subjected to a high temperature of from 950 to 1025 F. so that a. very substantial cracking of the vapors is effected. The resulting highly heated products are conducted into the upper portion of the enlarged vertical reaction chamber and passed downwardly therethrough in the manner referred to above. That application also discloses the simultaneous cracking of a light distillate such as naphtha along with the vapors removed from said enlarged separating chamber and subjected to cracking conditions in said coils.

The primary object of the present invention is to provide an improved cracking process of the general type disclosed in pending application Serial No. 153,900, but in which the lower boiling constitutents such as C4, C3, and C2 hydrocarbons are recovered and utilized in an improved manner.

A further object of the invention is to provide an improved process and apparatus for the conversion of distillate stocks into relatively high octane gasoline suitable for use in internal combustion engines of relatively high compression ratio.

Accordingly, the improved process of the present invention comprises a substantial modification of the process disclosed in pending application Serial No. 158,900, particularly in relation to the recovery of certain of the normally gaseous hydrocarbons by an absorption procedure. While the process of the present invention also includes the handling of crude oil charging stocks, it is more particularly directed to the recovery of C2, C3, and C4 hydrocarbons which are converted in the operation. In accordance with the proposed process, the gaseous hydrocarbon separated out from the conversion products produced in the operation and containing C2, C3 and C4 hydrocarbons are compressed to a relatively high pressure, mixed with liquid butane, cooled and then passed into the lower portion of a high pressure absorption tower where any constituents still remaining in the vapor state pass in countercurrent flow to a naphtha absorption menstruum introduced into the upper portion of the tower. The resulting mixture comprised mainly of C2, C3, and C4 hydrocarbons, including the introduced butane, is conducted at a high pressure to a thermal conversion zone where conditions are maintained suitable for the production of high anti-knock gasoline constituents.

Other features and advantages of the process and apparatus described in this application will be apparent to those skilled in the art from the following more detailed description thereof taken in connection with the accompanying drawing in which:

The single figure is a more or less convention-- al elevational diagram of a conversion unit particularly adapted for carrying out the improved process.

Referring to the drawing, the crude oil charging stock to be processed in accordance with the invention, is introduced through a line 2 and heated in a pipe still heater 4 to a temperature sufficient to vaporize substantially all of the gas oil and lower boiling constituents. The heated products are conducted from the heater 4 through a transfer line B into a crude oil fractionating tower 8 from which the gasoline is removed as vapor through a vapor line It). Various side streams are removed from the tower 8 as desired; for example, naphtha through a line I2, kerosene through a line l4, light gas oil or furnace oil through a line 16, and relatively heavy gas oil through a valved line N]. All of the side streams may be stripped of light constituents in the usual manner if desired.

The naphtha removed from tower 8 through line [2 is placed under pressure by a pump 23] mounted therein and conducted to the upper portion of an absorption tower 22, where the naphtha is used as an absorption medium to aid in recovering C2, C3, and C4 hydrocarbons produced in the conversion process of the present invention. The tower 22 may be of any usual construction and preferably provided with internal cooling coils as shown. The naphtha passes downwardly through the tower countercurrent to gases passing upwardly therethrough, and the naphtha together with the absorbed hydrocarbons referred to, pass through a line 24 into an accumulator tank 26 which is a supply tank for the butane or light distillate converter.

The crude oil bottoms or topped crude oil separated out in the tower 8 is withdrawn through a valved line 28 and passed by means of a pump mounted therein, into a supply tank or the bottom, or accumulator part of a high pressure fractionating tower 30 for the cracking unit. The introduced topped crude and reflux condensate produced in the tower 30 are collected together in the bottom thereof or in a separate tank, withdrawn through a line 32, and forced by means of a pump mounted therein through a heating coil, for example a parallel series of heating coils 34, 35 and 38, as mounted in a pipe still furnace 43. The charging stock to this furnace as introduced through the line 32, is heated to a temperature suiiicient to partially break the viscosity of the crude oil bottoms and vaporize the constituents of the type of gas oil and lower boiling hydrocarbons. The heated oil products are discharged from the heating coils 33, or other suitable heating coil, combined and passed through a transfer line 42 into a vaporliquid separator 54, from which the separated vapors are conducted through a line 46 into a second heating zone where the vapors are heated to a temperature of from about 935 to 985 F. This heating zone may comprise a bank of parallel heating coils 48 mounted in the convection section of the furnace 40. Where such a bank of parallel coils are used the vapors from the line 46 are uniformly distributed to the coils and heated for a sufiicient time to convert the vapors to unsaturated olefin type hydrocarbons. The highly heated products are conducted from the bank 48 through a transfer line 50 and passed to a further conversion coil, for example, in a pipe still heater 52, where the heated vapor products are mingled with higher temperature products resulting from the heating of the butane mixture from the tank 26.

The butane mixture to be heated in the pipe still heater 52 is conducted from the tank 26 through a line 54 and passed at a high pressure, preferably derived from that in the tank 26 or from a pump mounted in a by-pass line, to the heater 52. This heater may comprise a single heating coil of any desired form, but preferably consists of a plurality of parallel heating coils 56, 58 and 60 as shown. In these coils the butane fraction comprised mainly of C2, C3 and C4 hydrocarbons are heated to a high temperature of from 1050 to 1125 F., for example about 1075 F., and for a sufficient time to crack the light constituents sufficiently to produce a substantial proportion of olefin type hydrocarbons.

The highly heated products from the coils 60 are passed into a mixing line 62 where they are intimately mingled with the highly heated products from the transfer line 50. The resulting combined mixture of highly heated products are preferably conducted and distributed into a tube bank 64 comprising a plurality of similar parallel coils, although the heating may be done in a single coil. This tube bank 64 is mounted in the convection section of the furnace 52 and the products passed therethrough are subjected to an interpolymerization operation to polymerize the lower olefins with the higher boiling olefins. The resulting products at a temperature of the order of 1020 F. are discharged from the bank 64 through a transfer line 65 into the upper portion of a reaction chamber contained in a tower B8. The reaction chamber in the tower 68 is sufiiciently large to provide a relatively long time reaction on the vapor products which pass downwardly therethrough. As these products reach approximately the middle of the reaction chamber they are brought in contact with the separated crude oil residue from the separator 44 which is introduced into the chamber of tower 68 through a valve controlled line Ill. The residue from the separator 44 may be sprayed directly into the hot products in the tower 68 so that it receives a further viscosity breaking treatment if necessary.

After the desired reaction in the tower 68, the conversion products, together with any of the crude oil residue, are conducted through a funnel-like partition 12 and as they enter this funnel they are quickly cooled by relatively colder oil introduced from a spray head I4. This cooling operation is carried out to a suificient degree to prevent any coke forming reaction and condense all of the fuel oil type constituents which may be present in the tower or formed in the operation.

'The liquid residual oil is collected in the bottom of the tower 68 to keep a level below the funnel, and withdrawn at reduced pressure through a valved line I6 into a low pressure concentrator IS in which the hot fuel oil residue is distilled by the reduction in pressure. The amount of vaporization in the concentrator may be controlled so as to leave unvaporized a fuel oil of desired gravity which is withdrawn from the bottom of the still I8, while the vapors formed are passed overhead through a vapor line 88, condensed and collected in a receiver 82. Pro-vision is made for releasing any uncondensed. gas from receiver 82, while the condensate is conducted therefrom through a line 84 and forced by means of a pump mounted therein to spray head M where it is utilized as the cooling agent for the cracked products in the tower 68. A portion or all of the gas oil from the tower 8 and withdrawn through the line I8, is preferably introduced into the line 88 to condense vapors therein and to supply any additional cooling medium which may be required in the tower 88. The pump in the line I8 may be automatically controlled to maintain a definite level of oil in the receiver 82. The gas oil introduced into the line 88 acts as a menstruum for light constituents and thereby aids in the condensation of the vapors from the still 18 .as well as in the absorption of any low boiling hydrocarbons which may be present in these vapors.

The cracked vapor products which remain uncondensed by the cooling operation in the funnel I2 pass around the lower end of the funnel and up around the outside thereof to be discharged through a vapor line 88. These vapors may be washed and cooled to some extent by spraying oil from the line 84 through a spray ring 88 mounted around the neck of the funnel as shown. A considerable part of the oil introduced through I4 and 88 is vaporized and passed through vapor line 86. The vapors discharged through the line 86 and containing gas oil and lower boiling constituents are conducted into the lower part of the high pressure fractionating tower 38 in which the vapors are fractionated to hold back the constituents of higher boiling point than gasoline. The reflux condensate thus produced is collected in the base of the tower 30 and sent to the furnace 48 with the crude oil bottoms from the line 28 as described above.

The vapors discharged from the reflux tower 38 and containing the cracked gasoline constituents as well aslower boiling hydrocarbons are conducted through a vapor line 90, cooled and subjected to condensing conditions in a condenser 92 and the resulting gasoline condensate collected in a receiver 94. A portion of this gasoline may be returned to the top of the tower 30 to maintain the desired reflux ratio and end point of the overhead products. The mixture of gases such as hydrogen, C3, C2 and other hydrocarbons are withdrawn from the receiver 94 through an automaticpre'ssure valve controlled line 96 at a pressure of from 1'75 to 250 lbs. per square inch and further compressed to a higher pressure by the compressor mounted in this line, and then conducted into a butane supply line 98 by which liquid butane is introduced into the system of apparatus. The compressed gases from receiver 94 and the liquid butane introduced under high pressure through the line 98 are mixed, passed through a cooler and then' through a line I00 into the lower portion of the absorber 22. In these steps the liquid butane acts as a solution menstruum for C2 and C3 hydrocarbons,

The gasoline product recovered in the receiver 94 is withdrawn through a float valve controlled line I02 and forced at higher pressure by a pump mounted therein into a stabilizer I04 in which a portion of the C4 hydrocarbons as well as lower hydrocarbons are removed as vapors in order to provide a stabilized gasoline product. The stabilized gasoline is removed through a reboiler I86, which may be heated by any convenient means, and discharged from the system through a float valve controlled line I88. The vapors separated out in the tower I84 are conducted through a vapor line H9, cooled and subjected to condensing conditions, the resulting condensate, comprising mainly C2, C3 and C4 hydrocarbons being collected in a receiver I I2. A portion of the condensate collected in this receiver may be returned to the top of the stabilizer I84 to maintain the desired reflux ratio, and the vapor pressure and initial boiling point of the gasoline.

The uncondensed gases separated out in receiver H2 are conducted through an automatic pressure valve controlled line I I4 into the line 96, compressed and passed with the gases from receiver 9 3 to the absorber 22. The condensate collected in receiver II2 may be passed directly into line 54 but is preferably withdrawn through a line H8 and forced at high pressure by a float valve controlled pump mounted therein directly into the butane supply line 98 as shown, where it acts as a solution medium. Any vapors or gases which may be separated out in the accumulator tank 26 are conducted through a line II8 into the absorber 22.

While in the foregoing description mention is only made of the passage of gases from receivers 94 and H2 to the absorber 22, it is to be understood that other gases containing C2 or higher hydrocarbons produced at any other point in the system aresupplied to the compressor in the line 96, as for example from the receiver 82. A very high pressure of from 400 to 625 lbs. per square inch is maintained on the absorber 22, and it has been found that the light liquid hydrocarbons such as butane and other liquid hydrocarbons introduced through the lines 98 and H8 are very effective absorption agents for the C2 and. C3 hydrocarbons. The pressure on the tank 26 and absorber 22 as well as the included equipment, is preferably sufficiently high to force the charging stock through the line 54 and the pipe still heater 52 without the necessity of using a charging pump.

The charging stock introduced to the pipe still heater 52 through the line 54 comprises approximately butane, as introduced through the line 98, approximately of naphtha introduced through the line I2, while the remainder comprises mainly C2, C3 and C4 hydrocarbons introduced mainly through the lines 96 and I lb. The proportion of naphtha is kept to a minimum, or entirely removed from the stock prior to passing it to heater 52.

In carrying out the conversion operation, the pressure in receiver 94 is preferably maintained at from 175 to 250 lbs. per square inch, and from this receiver a back pressure is maintained in the preceding elements of the apparatus. The pressure in the crude oil tower 8 may be atmospheric or below, While the pressure in the stabilizer IE4 is preferably maintained at about 300 lbs. per square inch.

From the foregoing description of the process and cracking unit of the present invention, it will be apparent that certain modifications may be made without materially changing the nature of the operation. Such changes and alterations are contemplated within the scope of the invention as defined by the accompanying claims. It is to be further understood that the invention is not restricted to certain details of apparatus and of operation but that the features of the process claimed may be utilized in connection with other cracking units not involving the specific details herein disclosed.

Having thus described the invention in its preferred form, what is claimed is:

l. The improvement in the art of converting hydrocarbons for the production of relatively high anti-knock gasoline which comprises simultaneously and separately heating respectively lower and higher boiling point distillates than gasoline under thermal conversion conditions, converting the said distillates to products containing substantial proportions of unsaturated hydrocarbons, combining the resulting highly heated products from said separate heating and conversion conditions and subjecting them to further heating at a temperature of about 1020 'F. to effect interpolymerization of the products,

quickly cooling the resulting converted products to a temperature sufiiciently low to preventcoke formation and thereafter fractionating the constituents remaining in vapor form to produce a reflux condensate of higher boiling point than gasoline and separate out the gasoline hydrocarbons and a fraction containing C2, C3 and C4 hydrocarbons, separating the C2, C3 and a portion of the C4 hydrocarbons from the gasoline hydrocarbons, absorbing the separated C2, C3 and C4 hydrocarbons in a light solution absorbing menstruum containing a minor relatively small proportion of naphtha, and utilizing the resulting absorption mixture composed principally of C2, C3 and C4 hydrocarbons as .at least a portion of the charging stock of lower boiling point than gasoline for subjection to said thermal conversion conditions.

2. In the thermal conversion of petroleum oils into gasoline as defined by claim 1 in which crude oil is fractionated to produce naphtha, gas oil and crude oil bottoms, and in whichthe naphtha is utilized in small proportions as an absorption solution menstruum for C2, C3 and C4 hydrocarbons recovered in the conversion operation.

3. In the thermal conversion of petroleum distillates into gasoline as defined by claim 1 in which crude oil is fractionated to produce a plurality of fractions including gas oil and utilizing gas oil recovered from the crude oil as a cooling medium for quickly cooling the conversion products to a temperature below that of coke formation.

4. The improvement in the art of converting hydrocarbons for the production of relatively high anti-knock gasoline, which comprises simultaneously and separately heating respectively lower and higher boiling point distillates than gasoline under thermal conversion conditions, converting the said distillates to products containing substantial proportions of unsaturated hydrocarbons, combining the resulting highly heated products from said separate heating and conversion conditions and subjecting them to further heating at a temperature of about 1020 F. and efiecting interpolymerization of the products in a polymerizing Zone, quickly cooling the resulting interpolymerized products leaving said Zone to a temperature sulficiently low to prevent coke formation, thereafter passing the constituents remaining in vapor form into a fractionating tower to produce a reflux condensate of higher boiling point than gasoline and an overhead fraction containing gasoline and C2, C3, and C4 hydrocarbons, separating the C2, C3, and a portion of the C4 hydrocarbons from the said fraction, absorbing the separated C2, C2, and C4 hydrocarbons in a light solutionabsorbiug menstruum containing a minor relatively small proportion of naphtha, utilizing the resulting absorption mixture composed principally of C2, C3, and C4 hydrocarbons as at least a portion of the charging stock of lower boiling point than gasoline for subjection to said thermal conversion conditions, mixing crude oil bottoms with the reflux condensate produced in the iractionating tower and passing the resulting mixture through a heating zone and heating it to a temperature adapted to vaporize substantial proportions thereof, separating the resulting vapors from the unvaporized oil constituents and subjecting the vapors to heating and thermal conversion as the oil of higher boiling point than gasoline, and introducing separated unvaporized oil constituents while hot into the highly heated conversion products undergoing interpolymerization 'in said polymerizing zone.

5. A process forthermally converting relatively light oils into gasoline of relatively high antiknock value which comprises simultaneously heating a light distillate composed principally of C2, C3 and C4 hydrocarbons and an oil of higher boiling point than gasoline in separate heating zones, heating the light distillate in a stream of restricted cross section to a temperature sufiicient to efiect substantial conversion of the same to unsaturated hydrocarbons, heating the oil of higher boiling point than gasoline in a stream of restricted cross section to a temperature suihcient to efiect substantial conversion thereof to unsaturated hydrocarbons, mixing the resulting highly heated products and thereafter heating the resulting mixture in a stream of restricted cross section for a substantial period of time sufficient to interpolymerize the constituents of the mixture, thereafter conducting the highly heated products of the mixed stream into an enlarged reaction zone and passing the same 'tlierethrough at greatly reduced velocity, discharging the resulting highly heated converted products from said enlarged zone and separating any relatively high boiling tarry materials therefrom, fractionating the remaining vapors to produce a reflux condensate and a high anti-knock gasoline fraction, mixing crude oil bottoms with said reflux condensate and passing the resulting mixture through a heating zone in which it is heated to a temperature adapted to vaporize substantial proportions thereof, separating the resulting vapors from unvaporized oil constituents in a separating zone and supplying the vapors to the thermal conversion operation as said oil of higher boiling point than gasoline, and introducing the separated unvaporized oil constituents separated out 

